A commonly known method for cooling a liquid containing a volatile component is to supply the liquid to an atmosphere having a pressure which is lower than or equal to the saturated vapor pressure of the volatile component so that at least a portion of the volatile component is vaporized, whereby the liquid is cooled. In this case, if the liquid is low viscous or non-foaming, bubbles of the vaporized volatile component easily move upward in the liquid to reach the gas-liquid interface, and thereafter, burst and are released into the gas phase.
However, if the liquid is a foaming liquid containing a surfactant, bubbles which have reached the gas-liquid interface do not easily burst. Moreover, if the liquid is viscous, bubbles are retained or entrained in the liquid to form foam like shaving cream or meringue, resulting in a disadvantageous decrease in the density and flowability of the liquid.
To address these problems, methods of reducing the formation of foam and removing foam using a defoamer are known. However, defoamers often cannot be used in the fields of surfactants, sugars, thickener aqueous solutions, foods, etc.
Therefore, as a method for defoaming without using a defoamer, for example, PATENT DOCUMENT 1 describes a method of blowing, onto the surface of a liquid, a gas having a lower temperature than the solution temperature.
PATENT DOCUMENT 2 describes a method of, when blowing a liquid into an evaporator, evaporating the liquid in a pipe to produce a gas-liquid two-phase state, thereby reducing the formation of foam.
PATENT DOCUMENTS 3 and 4 describe a method of supplying a liquid to a degassing device where the pressure has been reduced and cooling the liquid as the liquid flows down along the inner wall surface of the degassing device, thereby condensing bubbles.
As a method for manufacturing an anionic surfactant, for example, PATENT DOCUMENT 5 describes a method of circulating an alkyl sulfate aqueous solution in a circulation path, continuously supplying alkyl sulfate and an alkali which are materials to the alkyl sulfate aqueous solution circulating in the circulation path to cause neutralization, and at the same time, continuously collecting a portion of the alkyl sulfate aqueous solution circulating in the circulation path as a product, and cooling the alkyl sulfate aqueous solution using a heat exchanger provided and inserted in the circulation path.
PATENT DOCUMENT 6 describes that by flashing a mixture obtained by contacting a sulfated material and a basic material together, the mixture is separated into a gas-phase component and a liquid-phase component, and the liquid-phase component is collected.
PATENT DOCUMENT 7 describes that an acid solution containing an acid precursor of an anionic surfactant and an alkali solution for neutralization are continuously supplied to a thin film evaporator to form a thin film of the mixture solution thereof on the heated inner wall of the evaporator while being subjected to neutralization and condensation/drying in parallel under reduced pressure.
PATENT DOCUMENT 8 describes a method for manufacturing alkyl ether sulfate in which alkyl ether is sulfated, followed by degassing under reduced pressure and then neutralization in a closed continuous scheme using an external cooling device.